Device for delivery of multiple liquid sample streams to a mass spectrometer

ABSTRACT

An electrospray apparatus employing multiple electrospray needles mounted on a rotatable plate sequentially delivers multiple sample streams to a mass spectrometer for analysis. The electrospray device includes an electrospray chamber, a rotatable needle supporting plate, a plurality of electrospray needles mounted on the plate, and a charger for applying a charge to droplets delivered to the electrospray chamber by the needles. The rotatable electrospray apparatus provides fast repetitive screening of simultaneously operating chromatography columns with a single mass spectrometer.

This application is a continuation of application Ser. No. 09/770,831,now abandoned, filed on Jan. 25, 2001, which is a continuation of Ser.No. 09/069,656, now U.S. Pat. No. 6,191,418, filed on Apr. 29, 1998which claims benefit of No. 60/079,622 Mar. 27, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to liquid delivery devices, and more particularly,the invention relates to devices for delivery of multiple liquid samplestreams to a mass spectrometer for screening of compound libraries.

2. Brief Description of the Related Art

In recent years, a large number of combinatory chemistry techniques havebeen developed which permit vast libraries of diverse chemical compoundsto be rapidly synthesized. In combinatory chemistry, a series ofchemical reactions is conducted, typically employing a plurality ofreagents at each step, to generate a library of compounds. Suchtechniques have the potential to greatly accelerate the discovery of newcompounds having biologically useful properties by providing largecollections of diverse chemical compounds for biological screening.

Mass spectrometry is emerging as an important tool for the interrogationof combinatorial libraries. To date, mass spectrometry has been used toassess library quality and, when coupled with molecular recognitiontechnologies, has allowed for some success in the isolation andcharacterization of active library compounds. Applications of massspectrometry have become increasingly important in combinatory chemistryand biological research.

Mass spectrometry obtains molecular weight and structural information onchemical compounds by ionizing the molecules and measuring either theirtime-of-flight or the response of the molecular trajectories to electricand/or magnetic fields. The electrospray process is one of the mostpromising techniques for producing gas phase molecular ions for a widerange of molecular entities.

According to a conventional electrospray process, a sample solutioncontaining molecules of interest and a suitable solvent is pumped ordrawn through an electrospray needle into an electrospray chamber. Apotential of up to several kilovolts may be applied to the needle togenerate a fine spray of charged droplets. Conversely, the needle may beheld at ground and the solution sprayed into an externally generatedelectric field. The droplets are typically sprayed into the chamber atatmospheric pressure. Optionally, this chamber houses gas lines (e.g.,N₂) to aid in the nebulization of the solvent stream and the disolvationor evaporation of solvent. The ions generated by the electrosprayprocess are then guided into the mass spectrometer by appropriateelectric field gradients. This typically requires multiple stages ofpumping for the removal of excess neutrals, such as solvent vapor.

With this conventional electrospray apparatus, the electrospray needleis connected to a single sample stream and delivers the moleculescontained therein by the electrospray process to the mass spectrometerfor analysis. When multiple sample streams are prepared, it is timeconsuming to switch between successive sample streams. This is due tothe fact that the available electrospray mass spectrometers are marketedwith a single electrospray needle. Therefore, switching streams involvesphysically breaking the connection between the needle and one samplestream, and re-establishing a connection with the next stream. Asidefrom the time involved in switching streams, the possibility exists forcross-contamination of the various streams.

It would be desirable to permit multiple sample streams from multiplechromatography columns or from other sample sources to be easilyconnected to the electrospray apparatus of a mass spectrometer forintermittent analysis of the sample streams from multiple columns. Itwould also be desirable to automatically move from analysis of onesample stream to another to analyze a plurality of sample streams in asshort a period of time as possible.

SUMMARY OF THE INVENTION

The present invention relates to an electrospray apparatus employingmultiple electrospray needles mounted on a rotatable plate tosequentially deliver multiple sample streams to a mass spectrometer foranalysis.

In accordance with one aspect of the invention, an electrospray devicefor a mass spectrometer includes an electrospray chamber, a rotatableneedle support, a plurality of electrospray needles mounted on therotatable needle support, and a charger. The electrospray needles areconnectable to a plurality of sample streams for delivery of droplets ofone of the sample streams at a time to a mass spectrometer orifice ofthe electrospray chamber. The charger applies a charge to the dropletsof the sample stream in the electrospray chamber and causes the dropletsto be focused into a beam passing through the orifice into the massspectrometer.

In accordance with another aspect of the present invention, a method isprovided for delivering a plurality of sample streams to a massspectrometer for analysis. The method includes the steps of: providing aplurality of sample streams to a plurality of electrospray needlesmounted on a rotating plate; continuously spraying the sample streamswith the electrospray needles; and sequentially positioning an outlet ofeach of the electrospray needles at delivery position for apredetermined dwell time by rotating and stopping the plate to deliverthe sample streams to the mass spectrometer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe preferred embodiments illustrated in the accompanying drawings, inwhich like elements bear like reference numerals, and wherein:

FIG. 1 is side view of a multiple needle electrospray apparatus fordelivery of sample streams to a mass spectrometer;

FIG. 2 is a top view of the multiple needle electrospray apparatus ofFIG. 1; and

FIG. 3 is a schematic top view of an alternative embodiment of amultiple needle electrospray apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A multiple needle electrospray apparatus for a mass spectrometerincludes a plurality of electrospray needles 10 mounted on a rotatableplate 12 for sequential injection of multiple sample streams. Therotatable electrospray apparatus allows collection of data from multiplesample streams by a single mass spectrometer 20 in a short time byrotating the electrospray apparatus to sequentially monitor the streamfrom each of the needles 10 for a brief duration before rotating theplate 12 to another of the needles. One example of a method forscreening compound libraries which involves analysis of multiple samplestreams by electrospray mass spectrometry is described in U.S. patentapplication Ser. No. 09/070,131, filed on Apr. 29, 1998, which isincorporated herein by reference in its entirety. According to oneapplication of this method, a compound library is prepared, such as bycombinatorial chemistry techniques. Multiple sample streams each ofwhich contain a compound library or sublibrary are passed through aplurality of frontal chromatography columns. Each stream being passedthrough a single column to analyze the interaction of members of thatsample stream with a target receptor within the column. The columnsinclude a solid support or inert material on which the target receptoris bound or coupled. As the sample stream is continuously infusedthrough the chromatography column, those compounds within the samplestream having a higher affinity for the target receptor (i.e., ligands)will be more strongly bound to the target receptors. When substantiallyall of the target receptors are filled, the compounds will break throughand begin to pass out of the column with those compounds having thelowest affinity passing out of the column first. The sample streamsexiting the chromatography columns are analyzed by electrospray massspectrometry to determine the break through time for each compound. Massspectrometry is particularly useful for this process because it allowsfor both detection and identification of the library members present inthe sample streams exiting the columns.

FIG. 1 illustrates a first embodiment of an electrospray device fordelivery of multiple liquid sample streams to the mass spectrometer 20.The electrospray device includes an electrospray chamber 14 for chargingthe droplets of a sample stream delivered by the electrospray needles 10and delivering the charged ions in a beam to the mass spectrometer 20.

The electrospray needles 10 each have an upper end mounted on therotatable plate 12 in the circular arrangement illustrated in the topview of FIG. 2. The lower ends of the electrospray needles may berotated into a reproducible delivery position within the electrospraychamber 14. The delivery position is at a precise location with respectto an orifice 22 of the mass spectrometer 20 which allows the sprayeddroplets to be focused into a beam passing through the orifice. Thedelivery position is preferably within about ±0.5 mm of an idealposition. In fluid connection with each of the electrospray needles 10is a sample source such as the chromatography columns 18 illustrated inFIG. 1. The chromatography columns 18 are preferably mounted on the topof the rotatable plate 12.

The electrospray chamber 14 surrounds the orifice 22 of the massspectrometer and is open to atmospheric pressure. The electrospraychamber 14 includes a front wall 28 having two vertically extendingslots 30 which allow the electrospray needles 10 to pass into and out ofthe electrospray chamber as the plate 12 is rotated. As illustrated inthe top view of FIG. 2, a top wall 32 of the electrospray chamber 14includes a semicircular opening 34 which receives a portion of therotatable plate 12.

The electrospray needles 10 are preferably coaxial needles which deliverthe sample stream through an inner needle lumen and deliver a nebulizergas, such as nitrogen, coaxially around the sample stream to break upthe flow of the sample stream into a spray of droplets. The electrospraychamber 14 includes a charged sampling plate 16 surrounding the massspectrometer entry orifice 22. The electrospray chamber 14 also includesan electrode 26 in the form of a half cylindrical portion of the frontwall 28 of the electrospray chamber. The charged sampling plate 16 andthe half cylindrical electrode 26 are charged with an electric potentialpreferably of about 0 to 6000 volts. The electric field established bythe sampling plate 16 and the electrode 26 surrounds the grounded needle10 and imparts a charge to the sprayed droplets.

According to an alternative embodiment of the invention, the charging ofthe sample stream droplets exiting the electrospray needle 10 may beaccomplished by use of a charged electrospray needle in place of thecharged sampling plate 16 and electrode 26. The needle 10 may becontinuously charged or may be charged only when the needle reaches thedelivery position within the electrospray chamber 14 by an electricalcontact.

A counter current drying gas, such as nitrogen, is delivered to theelectrospray chamber 14 through a passageway 24 between the chargedsampling plate 16 and the entry orifice 22 to assist in desolvating orevaporating the solvent from the sample stream to create fine droplets.According to an alternative embodiment of the invention, the drying gasmay be delivered to the electrospray chamber 14 in manners other thanthrough the passageway 24. In addition, the nebulizer gas may bedelivered to the electrospray chamber 14 separately rather than by aco-axial flow through the electrospray needle. Both the nebulizer gasand the drying gas are introduced into the electrospray chamber 14 toobtain fine droplets of the sample stream. However, depending on theflow rate of the sample stream, the fine droplet size may be achievedwithout the need for a nebulizer gas and/or a drying gas.

The rotatable plate 12 is rotated by a motor connected to a drive shaft36 of the plate. Preferably the motor is interfaced with a controller tocontrol the rotation of the plate and the dwell times for each of theneedles. Although the rotatable plate 12 has been illustrated as acircular plate, it should be understood that other plate shapes, such asmulti-sided plates, rings, and the like, may be used without departingfrom the invention.

In operation, multiple sample streams are continuously delivered to eachof the chromatography columns 18 from sample sources by, for example, apump, such as a syringe pump. The sample streams exiting the columns 18may be combined with a diluent in a mixing chamber or mixing tee 38positioned between the column and the needle 10. The sample streams passcontinuously through the electrospray needles 10 with a nebulizer gasdelivered around the sample streams to break up the flow into droplets.Sample streams pass through all of the needles 10 simultaneously withonly one of the streams from a needle positioned at the deliveryposition being analyzed by the mass spectrometer at a time. The samplestreams from the remaining needles 10 are collected by a tray 40 fordelivery to waste or for reuse.

To perform analysis of the multiple sample streams, one embodiment ofthe invention provides that the rotatable plate 12 is stepped in onedirection, e.g., counter clockwise, through approximately half of theneedles 10. When a quadrupole mass spectrometer is used a dwell time foreach electrospray needle 10 ranges from about 0.5 to 10 seconds,preferably about 1 to 5 seconds before switching to the next column.After analysis of approximately half the sample streams, the rotatableplate 12 then returns clockwise to a home position and begins steppingin an opposite direction, e.g., clockwise, through the remaining half ofthe needles 10. Finally, the rotatable plate 12 returns again to thehome position and repeats the procedure. The system operatescontinuously for a preset period of time related to the chromatographicrequirements. Step times for rotation between successive needles ispreferably about 10 to 100 msec. The rotation of the plate 12 in onedirection followed by reversing the rotation is preferred to prevent thefeed lines for feeding the sample streams from the pump to the columns18 from becoming twisted.

According to an alternative embodiment of the invention, the samplesource, the pump or alternative, and the feed lines for delivery of thesample streams to the columns 18 may be mounted on the plate 12. Withthis embodiment, the plate 12 will be rotated continuously in onedirection to sequentially analyze the flows from each of the needleswithout requiring the plate to reverse direction and return to a homeposition.

The mass spectrometer for use with the present invention may be any ofthe known mass spectrometers including a quadrupole mass spectrometer,quadrupole ion trap mass spectrometer, Penning or Paul ion trap massspectrometer, FTICR (Fourier transform inductively coupled resonance)mass spectrometer, time-of-flight mass spectrometer, and the like. Atime-of-flight mass spectrometer is preferred due to its high spectralacquisition rate (>100 spectra per second). However, the slowerquadrupole mass spectrometer may also be used which can record spectraat a rate of approximately 0.5 to 1 per second. The dwell times foranalysis of each sample stream will vary depending on the spectralacquisition of the mass spectrometer used.

FIGS. 1 and 2 illustrate an electrospray device for analysis of samplestreams from ten columns. When the electrospray device having tencolumns is employed with a quadrupole mass spectrometer with analysis ata rate of about 1 spectrum per second and a dwell time of about 5seconds per column is used, the system will take about 5 spectra fromeach column at a time and will cycle through all the columns inapproximately 60 seconds.

Alternative embodiments of the invention may include different numbersof electrospray needles depending on the number of sample streams whichare to be analyzed. The spacing of the multiple electrospray needles 10is important to the operation of the electrospray device. In particular,the electrospray needles 10 should be spaced sufficiently to preventcross over effects resulting from the sample stream from one columnsinfluencing the analysis of the sample stream of an adjacent column. Inaddition, the electrospray needles 10 should be spaced as close togetheras possible to minimize the step times for rotation between adjacentneedles. Preferably, the spacing between columns should be about 0.5 cmto 10 cm, depending on the mass spectrometer used.

FIG. 3 is a top view of an alternative embodiment of a rotatableelectrospray apparatus for delivery of sample streams to a massspectrometer 120. The electrospray apparatus includes a plurality ofelectrospray needles 110 mounted in a radial arrangement on a rotatableplate 112. Each of the needles 110 are in fluid connection with achromatography column 118. The radial arrangement of the electrosprayneedles 110 allows more columns 118 to be positioned on a rotatableplate 112 of a smaller diameter. According to this embodiment, thedischarge ends of the needles 110 are preferably spaced a distancesufficient to prevent a cross over effect between adjacent needlesHowever, the columns 118 can be arranged close together around theperiphery of the rotatable plate 112.

The orientation and arrangement of the rotatable plate 12, the columns18, and the electrospray needles 10 may be varied to achieve manydifferent angular relationships for use with different types of massspectrometers. For example, the rotatable plate 12 may be positionedvertically and the columns 18 and needles 10 may be positionedhorizontally. In addition, for some types of mass spectrometers theelectrospray chamber is not enclosed by walls.

The present invention provides distinct advantages over prior artmethods of operating and screening one column at a time. The rotatableelectrospray apparatus allows multiple sample streams to be easilydelivered to a single mass spectrometer and provides fast repetitivescreening of simultaneously operating columns with a single massspectrometer.

While the invention has been described in detail with reference to thepreferred embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made and equivalentsemployed, without departing from the present invention.

What is claimed is:
 1. A method of analyzing each of a plurality offluid samples, comprising: simultaneously spraying a plurality of fluidsamples from needles of an electrospraying needle array; charging thefluid samples from the electrospray needle array one at a time anddelivering the charged fluid samples to a mass spectrometer; andanalyzing the mass spectrum of the plurality of fluid samples.
 2. Themethod of claim 1 further including the step of positioning a device toblock all but one of the plurality of fluid samples from reaching themass spectrometer by positioning the device between the electrosprayneedle array and the mass spectrometer.
 3. The method of claim 1,wherein analyzing comprises: generating a continuous mass spectrumreading over a period of time; and sampling the continuous mass spectrumreading at moments in time when each fluid sample is analyzed; therebygenerating a separate mass spectrum reading for each of the plurality offluid samples over a period of time.
 4. The method of claim 1, whereinthe fluid samples sprayed in the spraying step are liquid samples. 5.The method of claim 1, wherein the step of charging includes the use ofa charged sampling plate and an electrode disposed within a samplingchamber, the sampling chamber connected to the mass spectrometer entryorifice.
 6. A method of analyzing each of a plurality of liquid samples,comprising: simultaneously spraying a plurality of liquid samples fromneedles of an electrospraying needle array; charging the liquid samplesfrom the needles one at a time; positioning a device to collect all butone of the liquid samples; moving the electrospray needle array anddevice relative to one another to permit the charged liquid samples toreach the mass spectrometer one at a time; and analyzing the massspectrum of the plurality of liquid samples.
 7. The method of claim 6wherein positioning a device comprises positioning the device betweenthe electrospray needle array and the mass spectrometer.
 8. The methodof claim 6, wherein analyzing comprises: generating a continuous massspectrum reading over a period of time; and sampling the continuous massspectrum reading at moments in time when each fluid sample is analyzed;thereby generating a separate mass spectrum reading for each of theplurality of liquid samples over a period of time.